Common answering techniques (Combined Chemistry)

Samuel’s Chemistry Notes #A1ForChem Common answering techniques (Combined Chemistry) Chemical Bonding 1. Explain why sodium chloride has a high melting point. Ans: Sodium chloride has a giant ionic crystal lattice structure . Large amounts of energy is used to overcome the strong electrostatic forces of attraction between oppositely charged ions . Therefore, sodium chloride has high melting points. 2. Explain why ammonia has a low melting point. Ans: Ammonia has a simple covalent structure . Small amounts of energy is used to overcome the weak intermolecular forces of attraction between molecules . Therefore, ammonia has low melting points. Combining 1 & 2 together … 3. At room temperature and pressure, ammonia exists as a gas while sodium chloride exists as a solid. Explain why. Ans: Ammonia has a simple covalent structure . Small amounts of energy is used to overcome the weak intermolecular forces of attraction between molecules . Therefore, ammonia exists as a gas at room temperature and pressure. Sodium chloride has a giant ionic crystal lattice structure . Large amounts of energy is used to overcome the strong electrostatic forces of attraction between oppositely charged ions . Therefore, sodium chloride exists as a solid at room temperature and pressure.

Samuel’s Chemistry Notes #A1ForChem 4. In molten state, sodium chloride conducts electricity. However, in solid state, sodium chloride is unable to conduct electricity. Explain why. Ans: In solid sodium chloride, ions are held together by strong electrostatic forces of attraction . However, when sodium chloride enters a molten state, the giant ionic crystal lattice structure is broken down , and ions are now mobile to act as charge carriers to conduct electricity . 5. Why does ammonia not conduct electricity in ANY state? Ans: Ammonia has a simple covalent structure . In this simple covalent structure, all the electrons have been used up for covalent bonding . Therefore, there are no electrons to act as charge carriers , thus ammonia cannot conduct electricity .

Samuel’s Chemistry Notes #A1ForChem Chemical Energetics 1. How will increasing the temperature of the reactants affect the rate of reaction? Ans: By increasing the temperature of the reactants, the reacting particles will become more energetic, which means they have higher amounts of kinetic energy . Therefore, this means that more particles will have energy equal to or greater than the activation energy , thus the rate of reaction will increase. 2. Why does grinded magnesium react more quickly than magnesium lumps? Ans: When magnesium is grinded, it has a smaller particle size, meaning it has a greater surface area exposed for collisions. This increases the frequency of effective collisions , increasing the rate of reaction.

Samuel’s Chemistry Notes #A1ForChem Maintaining Air Quality Carbon cycle: Carbon dioxide is released through combustion of (carbon containing) fuels / respiration / decomposition / decay; Carbon dioxide is taken in through photosynthesis / ocean uptake; If carbon dioxide released is more than carbon dioxide taken in, there will be a net increase in carbon dioxide in the atmosphere / Carbon dioxide released will be balanced by or is equal to the carbon dioxide taken in.